[request] Ensure base_url() always has a trailing '/' (closes #3955093) Just as an example, cubicweb.ajax.js is clearly written under the assumption that BASE_URL/baseuri() - which simply contains req.base_url() - has a trailing /.

if not rql('CWConstraintType X WHERE X name "RQLUniqueConstraint"',
           ask_confirm=False):
    rql('INSERT CWConstraintType X: X name "RQLUniqueConstraint"',
        ask_confirm=False)